1. Field of the Invention
This invention relates in general to the field of dentistry, and in particular, to a novel method and novel apparatus for constructing dentures.
2. Prior Art
In the construction of dentures, one of the most significant problems is to orient the upper and lower casts, in which the artificial teeth are set, relative to one another, in such a manner that the movements of the mandible and its neuro-muscular influences will be modeled in a true and reproducible form. Such movements, or registrations, must not only be reproducible, but definite and durable as well. Further, once such registrations are made, it must be possible to transfer the registrations to an instrument such as an articulator, without introducing any error, in order to actually construct a dentition that will be in agreement with the original registrations of jaw movement.
The human jaw is capable of the widest variety of movements. Modelling such movements is complicated by the fact that the lower jaw is not merely connected by a hinge, and is capable of translational movement as well. Accordingly, when seeking to model or reproduce such movement, one must be concerned with rotary or hinge-like motion, which depends upon the centers of rotation of the condoyles with respect to the glenoid fossa, as well as translational motion, which results from motion of the condoyle along the articular eminence. Other movements result from the combination of rotary and translational motion, as well as from bodily (mandibular) motion, or Bennett movement. To further complicate matters, all of the foregoing are controlled to some extent by biological factors in the formation of ligaments, meniscus and musculature, emotional factors and habit patterns, as well as the shape of the bony structures, including condoyle, articular eminence, articular fossa and incisal guidance, if present. Incisal guidance is not present as such in totally edentulous mouths.
All of the foregoing factors contribute to the definition of a three dimensional envelope of motion, which defines or describes all of the natural movements of the jaw for any particular person.
Intra oral tracing apparatus are known which utilize moldable material and scribing pins for forming what are called gothic arch traces. A set of at least three such gothic arch traces, made in accordance with relative movements of the human jaw, accurately define the three dimensional envelope of motion described above. Although some such apparatus are known, their accuracy has been to limited avail, because no articulators are known in the art which can utilize such gothic arch traces in a manner which precisely models or reproduces the three dimensional envelope of motion unique to each individual.
This deficiency in the prior art is due to an unjustified belief that the solution lies in the development of a so-called universal articulator, which is capable of reproducing each and every movement of each and every jaw. The prior art is replete with such articulators, each of which utilizes some form of hinged or pivotal connection in order to simulate movement between upper and lower dentures, and therefore upper and lower jaws.
In a distinct departure from this prior art, this invention teaches the elimination of the so called universal articulator, and instead, teaches a means by which an articulator may be programmed or calibrated to suit each individual patient, the method and apparatus being not only as accurate as humanly possible, but being quick and inexpensive as well. In the construction of dentures, a method for calibrating an articulator, according to this invention, comprises the steps of forming a set of intra oral gothic arch traces, the traces defining a three dimensional envelope of motion, and utilizing the intra oral traces to form a substantially identical set of gothic arch traces on the articulator, whereby relative movement of the articulator may be confined to the envelope of motion. An articulator according to this invention for constructing dentures, for use with a gothic arch tracing apparatus, comprises first and second members, having means for holding the members in spaced relationship, without being connected, and having means for mounting dental casts between the members, said casts having tracing apparatus disposed therein, in operable relationship, and means for forming a set of gothic arch traces, for controlling relative movement of the members, in accordance with movement of the tracing apparatus.
Only one unhinged articulator is known in the art, however, it too seeks to be a universal articulator, by reason of its reliance on removable analog blocks to define movement of the articulator. Further, this articulator has upper and lower frames, each of which has a defined horizontal axis of rotation and a centric reference device for centering the upper frame laterally with reference to the lower frame. Such predefined axes and references introduce errors into the modelling process before it has even begun. By way of contrast, the method and apparatus taught herein make no such predefinitions, and are therefore significantly more accurate.